TASK DEFINITION: In this task, you are given an article. Your task is to summarize the article in a sentence.
PROBLEM: It's like combustion in reverse, and in essence it is what powers plants: CO2 and water in, energy-rich sugar molecules out.
But in matters of energy, nothing comes for free.
Just as plants need sunlight to pull off the trick, Air Fuel Synthesis, the firm profiled in the UK's Independent newspaper, need to use good old-fashioned electric energy to pull off theirs.
As with any novel fuel production or energy storage method, it is the numbers that matter: efficiency is king.
The degree to which this technique can fulfil its promise to lower CO2 and provide a sustainable fuel source depends crucially on the balance of energy it requires and the energy it stores.
First things first - squashing CO2 back into a molecule packed with energy is not a new idea.
For example, work done at Princeton University in the US and published in 1994 to make the fuel additive methanol from CO2 has more recently been refined and spun into a company called Liquid Light that is aiming to do the same thing.
In Iceland, Carbon Recycling International opened a plant at the end of 2011 drawing waste CO2 from a power station, with capacity to produce five million litres of methanol per year.
Air Fuel Synthesis build on these methods by turning the methanol into something more like petrol, using processes well entrenched already in the petroleum industry.
The firm, so far, has made five litres of their fuel in a two-year demonstration experiment in which they have invested Â£1m.
Peter Harrison, the firm's chief executive, told BBC News that the demonstration did not focus on efficiency, but rather a proof of principle.
"All we're trying to demonstrate is that here in the UK we can make petrol from air," he said.
"[These processes] are all capable of working at industrial scale, and we've brought it down to container scale. There' a lot of work to do to develop the supply chains and to reduce the costs.
"We've got a design now for a one-tonne-a-day unit, and we expect to be in production by 2015."
Their first market is "greening the motorsport industry" by offering their pure fuels to racing teams.
But in the bigger picture, the petrol-from-air idea joins a legion of others that are trying to crack the far bigger problem of storing energy produced by renewable sources.
Like the recently reported "liquid air" approach, Air Fuel Synthesis wants to use renewable energy which may come when there is no consumer demand for it.
Mark Carpenter, research fellow at Cranfield University's Chemical Safety, Fuels and Environment Group, said that hydrocarbon fuels were "a very good way of storing energy" but that linking the process to renewable energy was the only way to make it tenable.
"If they can get enough renewable, low-cost electricity, that's a big determinant," he told BBC News. "It could be a very clean and green way of producing hydrocarbon fuels."
"But it'll be a minority player in terms of trying to meet global fuels demand - very, very small.
"It's certainly interesting that someone's considered this as a method, it's just whether you can make the chemistry work and get a reasonable degree of efficiency."
As with many other energy production and storage methods, only time and market forces will determine how far the petrol-from-air idea can go.

SOLUTION: An idea has hit the news on Friday to produce petrol from air and water - removing CO2 from the atmosphere, combining it with hydrogen split from water vapour and turning it into a fuel that can go straight back into the petrol tank.

PROBLEM: The Nigerian military has been in overdrive in trying to control the narrative of its war against Boko Haram in recent weeks.
It says it has cornered the jihadists and the conflict will soon be over - in line with its mandate from President Muhammadu Buhari to end the crisis by mid-November.
Boko Haram's eccentric frontman Abubakar Shekau has not appeared in a video since February, when he threatened to disrupt the elections.
The following month he pledged allegiance to the Islamic State group (IS) in an audio message and since IS also reached out to their Nigerian counterpart, Shekau has taken a back seat.
Shekau has released similar audio clips to disprove reports about his death, although the fact that he is not visible leaves room for speculation among the army that they have killed him, as they have claimed on several occasions.
His retreat from the forefront signifies that Boko Haram, also known as IS West Africa Province, now takes orders from the further up the IS hierarchy.
Nonetheless, there was recently room for another message to once again defy the Nigerian government, which sparked the realisation in the military that this game of cat-and-mouse was going nowhere.
Defence spokesman Colonel Rabe Abubakar described Shekau as "irrelevant" and urged Nigerians "not to lose sleep over the concocted audio rhetoric of the waning terrorist sect which is a usual antic of a drowning person struggling to hold on to anything to remain afloat".
Overall, Boko Haram's propaganda campaign has waned since the beginning of the year, when it used social media to promote sleek videos showing speeches and attacks.
The latest video, released to coincide with the Eid al-Adha festival in late September, is poorly produced and appears to show fighters praying but there is no indication of how recent all the footage is.
It has been two years since the US placed a $7m (Â£4.5m) bounty on Shekau's head but neither he nor his top commanders have been found.
As long as that is not achieved, the group will be able to rethink its strategy, recruit, rearm and develop new methods of operating.
The jihadists have shown that they can continue to inflict significant damage even with few but deadly explosions.
In one recent triple attack, they killed more than 100 people in Maiduguri, the capital of Borno state, where they were formed in 2002.
Using football to tackle Boko Haram
Who are Boko Haram?
The global concern for the missing Chibok schoolgirls still gives Boko Haram a bargaining chip.
The news of their abduction grabbed the world's attention in a way the deaths of thousands before were unable to.
The resulting scrutiny, as well as criticism from human rights organisations, means that the Nigerian military has taken a more cautious approach to the conflict than it did in the early days, when there were frequent allegations that the military was involved in widespread human rights abuses.
The new chain of command means that it is now more difficult than ever before for the insurgent group to agree to dialogue with the government
As the conflict escalated, Nigeria needed cooperation from its neighbours to secure the borders but this would inevitably come at a cost for Cameroon, Chad and Niger.
Each of these allies has now been attacked, as the IS militants look to extend their reach in West Africa.
Nigeria remains a priority for the Islamist fighters but what was initially a local conflict is changing.
If indeed Boko Haram is defeated in Nigeria, the fact that the group is now part of a wider international network means the campaign of violence could escalate in the neighbouring countries, particularly Chad and Niger, which have broader expanses of land, far more porous borders and are closer to Libya, where IS began its expansion in Africa.
For now, the coalition of the African Union-backed Multinational Joint Task Force should be reminded that a wane in the intensity of Boko Haram attacks says little about the strength of the group as a whole.
While aiming to end the conflict, President Buhari should learn from the mistakes of his predecessor, Goodluck Jonathan, who gave a series of failed deadlines to defeat the militants.
Mr Buhari's government, like many Nigerians, will be hoping for a speedy resolution but by now they know better than to be naive.

SOLUTION: Nigeria predicts that Boko Haram will soon be defeated, but the militant group's ties with Islamic State mean that would probably push the fighters further into neighbouring countries, writes BBC Monitoring Africa security correspondent Tomi Oladipo.

PROBLEM: Berlin Mayor Klaus Wowereit told a ceremony on Bernauer Street: "The Wall is history but we must not forget it."
President Christian Wulff said Germany had been securely established as a reunified country.
The city observed a minute's silence at noon (10:00 GMT) in memory of those who died trying to escape.
Wall sickness: Berlin's unique illness
Soldiers from the East began construction on the morning of 13 August 1961.
The BBC's Stephen Evans in Berlin says the East German authorities portrayed the Wall as a barrier to keep the fascist West out - what came to be known as the Anti-Fascist Protection Rampart.
But he says the accepted view now is that it was to keep East German potential migrants in.
Addressing the ceremony on Bernauer Street, famously divided by the Wall and now site of a memorial, Mayor Wowereit said the capital was remembering the "saddest day in its recent history".
"It is our common responsibility to keep alive the memories and pass them on to the next generation, to maintain freedom and democracy and to do everything so that such injustices may never happen again," he said.
At a ceremony at a former crossing-point, President Wulff said the wall had been "an expression of fear" of those who created it.
"The world situation, of which this wall was a symbol, seemed irreversible to many people," he said.
"But this was not the case. In the end, freedom is unconquerable. No wall can survive the will for freedom in the long term. The violence of just a few has no hold over the drive for freedom of many."
Chancellor Angela Merkel, who also attended the event, was herself raised in the East.
The number of people who died trying to cross the Wall is disputed - at least 136 are known to have been killed but victims' groups say the true number is more than 700.
The Berlin Wall
The first victim was thought to be Guenter Litfin on 24 August 1961 and the last Chris Gueffroy on 6 February 1989.
A list of names of the victims was read out overnight.
Although the Wall came down in 1989, it remains for some a symbol of continuing economic division between the richer west and poorer east.
Brigitta Heinrich, a schoolteacher by profession, grew up in Klein-Glienicke, which was unusual in that it was an East German enclave on the territory of West Berlin.
Speaking to Russian news agency Ria-Novosti, she said one of her own pupils had escaped across the Wall in the early days, using a ladder.
The schoolboy's parents were forced to move out of Klein-Glienicke as a result, and the mother was sacked from her job in a company, she said.
Recalling the hardships and broken illusions of the communist state, Ms Heinrich, who still lives in the East, also talked of the difficulty of readjusting to a unified country.
She said she had made friends with other Europeans such as Italians and Finns since the fall of the Wall but some West Germans, especially in regions further away from Berlin, seemed indifferent to people from the former East, as if an invisible barrier remained.
"I cannot name a single West German with whom I socialise now - really, I can't," she said.
Few parts of the Wall remain, though city authorities have laid down an 8km (five-mile)row of cobblestones to mark its path.
Tourists often struggle to find original sections.

SOLUTION:
Germany is marking 50 years since the building of the Berlin Wall when the communist East closed its border, dividing the city for 28 years.

